Convert system/core to Result::ok()

No functionality changes, this is a mechanical cleanup.

Test: m
Test: cd system/core && atest
Change-Id: Ifdaa3ce1947ed578f656d5a446978726eb416c36
diff --git a/init/selinux.cpp b/init/selinux.cpp
index 852d6ca..41007c1 100644
--- a/init/selinux.cpp
+++ b/init/selinux.cpp
@@ -477,7 +477,7 @@
         }
     }
 
-    if (auto result = WriteFile("/sys/fs/selinux/checkreqprot", "0"); !result) {
+    if (auto result = WriteFile("/sys/fs/selinux/checkreqprot", "0"); !result.ok()) {
         LOG(FATAL) << "Unable to write to /sys/fs/selinux/checkreqprot: " << result.error();
     }
 }